feat: support duplication of frames to multiple devices

[chris-piekarski]

Note

Adds multi-device output for Linux v4l2loopback (single conversion, duplicated writes) and updates CI to drop Windows builds and publish wheels to GitHub Releases.

• Linux backend (v4l2loopback):
  • VirtualOutput: support multiple devices (_camera_fds, _camera_devices); write frames to all; improved auto-detect, validation, and cleanup; device() returns comma-separated list.
  • Pybind layer (native_linux_v4l2loopback/main.cpp): accept device as generic Python object; parse string or sequence into device list; default to None.
  • Python API (pyvirtualcam/camera.py): device now Union[str, List[str]] on Linux; normalize list for v4l2loopback; docs clarify multi-device usage.
• Examples:
  • Add examples/multi_device.py demonstrating single vs multi-device usage and frame duplication.
• CI:
  • Remove Windows build/test matrix and related steps.
  • Add publish-wheels job to create GitHub Release and upload built wheels on version tags.
  • Docs job installs wheel from artifacts; add publish-docs (GitHub Pages) on tags.

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